/*
 * Copyright (c) 2007-2012, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */
/*
 * Copyright 1999-2004 The Apache Software Foundation.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
/*
 * $Id: DTMStringPool.java,v 1.2.4.1 2005/09/15 08:15:05 suresh_emailid Exp $
 */

package com.sun.org.apache.xml.internal.dtm.ref;

import java.util.Vector;

import com.sun.org.apache.xml.internal.utils.IntVector;

/** <p>DTMStringPool is an "interning" mechanism for strings. It will
 * create a stable 1:1 mapping between a set of string values and a set of
 * integer index values, so the integers can be used to reliably and
 * uniquely identify (and when necessary retrieve) the strings.</p>
 *
 * <p>Design Priorities:
 * <ul>
 * <li>String-to-index lookup speed is critical.</li>
 * <li>Index-to-String lookup speed is slightly less so.</li>
 * <li>Threadsafety is not guaranteed at this level.
 * Enforce that in the application if needed.</li>
 * <li>Storage efficiency is an issue but not a huge one.
 * It is expected that string pools won't exceed about 2000 entries.</li>
 * </ul>
 * </p>
 *
 * <p>Implementation detail: A standard Hashtable is relatively
 * inefficient when looking up primitive int values, especially when
 * we're already maintaining an int-to-string vector.  So I'm
 * maintaining a simple hash chain within this class.</p>
 *
 * <p>NOTE: There is nothing in the code that has a real dependency upon
 * String. It would work with any object type that implements reliable
 * .hashCode() and .equals() operations. The API enforces Strings because
 * it's safer that way, but this could trivially be turned into a general
 * ObjectPool if one was needed.</p>
 *
 * <p>Status: Passed basic test in main().</p>
 * */
public class DTMStringPool {
    Vector m_intToString;
    static final int HASHPRIME = 101;
    int[] m_hashStart = new int[HASHPRIME];
    IntVector m_hashChain;
    public static final int NULL = -1;

    /**
     * Create a DTMStringPool using the given chain size
     *
     * @param chainSize The size of the hash chain vector
     */
    public DTMStringPool(int chainSize) {
        m_intToString = new Vector();
        m_hashChain = new IntVector(chainSize);
        removeAllElements();

        // -sb Add this to force empty strings to be index 0.
        stringToIndex("");
    }

    public DTMStringPool() {
        this(512);
    }

    public void removeAllElements() {
        m_intToString.removeAllElements();
        for (int i = 0; i < HASHPRIME; ++i)
            m_hashStart[i] = NULL;
        m_hashChain.removeAllElements();
    }

    /** @return string whose value is uniquely identified by this integer index.
     * @throws java.lang.ArrayIndexOutOfBoundsException
     *  if index doesn't map to a string.
     * */
    public String indexToString(int i) throws java.lang.ArrayIndexOutOfBoundsException {
        if (i == NULL)
            return null;
        return (String) m_intToString.elementAt(i);
    }

    /** @return integer index uniquely identifying the value of this string. */
    public int stringToIndex(String s) {
        if (s == null)
            return NULL;

        int hashslot = s.hashCode() % HASHPRIME;
        if (hashslot < 0)
            hashslot = -hashslot;

        // Is it one we already know?
        int hashlast = m_hashStart[hashslot];
        int hashcandidate = hashlast;
        while (hashcandidate != NULL) {
            if (m_intToString.elementAt(hashcandidate).equals(s))
                return hashcandidate;

            hashlast = hashcandidate;
            hashcandidate = m_hashChain.elementAt(hashcandidate);
        }

        // New value. Add to tables.
        int newIndex = m_intToString.size();
        m_intToString.addElement(s);

        m_hashChain.addElement(NULL); // Initialize to no-following-same-hash
        if (hashlast == NULL) // First for this hash
            m_hashStart[hashslot] = newIndex;
        else
            // Link from previous with same hash
            m_hashChain.setElementAt(newIndex, hashlast);

        return newIndex;
    }

    /** Command-line unit test driver. This test relies on the fact that
     * this version of the pool assigns indices consecutively, starting
     * from zero, as new unique strings are encountered.
     */
    public static void _main(String[] args) {
        String[] word = { "Zero", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen", "Twenty", "Twenty-One", "Twenty-Two", "Twenty-Three", "Twenty-Four", "Twenty-Five", "Twenty-Six", "Twenty-Seven", "Twenty-Eight", "Twenty-Nine", "Thirty", "Thirty-One", "Thirty-Two", "Thirty-Three", "Thirty-Four", "Thirty-Five", "Thirty-Six", "Thirty-Seven", "Thirty-Eight", "Thirty-Nine" };

        DTMStringPool pool = new DTMStringPool();

        System.out.println("If no complaints are printed below, we passed initial test.");

        for (int pass = 0; pass <= 1; ++pass) {
            int i;

            for (i = 0; i < word.length; ++i) {
                int j = pool.stringToIndex(word[i]);
                if (j != i)
                    System.out.println("\tMismatch populating pool: assigned " + j + " for create " + i);
            }

            for (i = 0; i < word.length; ++i) {
                int j = pool.stringToIndex(word[i]);
                if (j != i)
                    System.out.println("\tMismatch in stringToIndex: returned " + j + " for lookup " + i);
            }

            for (i = 0; i < word.length; ++i) {
                String w = pool.indexToString(i);
                if (!word[i].equals(w))
                    System.out.println("\tMismatch in indexToString: returned" + w + " for lookup " + i);
            }

            pool.removeAllElements();

            System.out.println("\nPass " + pass + " complete\n");
        } // end pass loop
    }
}
